The North Norwich Cluster Calculations Policy

The North Norwich Cluster Calculations Policy
September 2014

The Ethos and Aims of the Policy
To learn and make progress in mathematics, children need to be provided with a rich mixture of language, representations and experiences to enable them to form their own relational understanding of the subject . If children are to develop a relational understanding of the mathematics that they are using in lessons, then they need to have a series of internal representations that they can draw on to help them construct their own understanding of the concept. This conceptual understanding is made by the forming of many connections between mental representations which in turn are made when the child reasons about the resource that they are using. It is important to remember that there isn’t any maths in a resource, the maths is brought to the resource by the teacher and the child interacting with it. Maths is a subject that can be made sense of, not a series of procedures that is to be memorised. Aims: This policy should show the natural progression that a child should make through their mathematical education, not a year by year guide. Written methods that are taught should help children to make internal representations which will support future mental calculation. This policy will show how we calculate, not what we calculate in the North Norwich Cluster.

Models and Images for Understanding Addition and Subtraction
Addition - Phase 1 Combine sets of objects in practical ways. Count all, and then count on. Make connections with counting up a number track. Lay out objects beneath a number line/ number track to make the connection between the two. Subtraction – Phase 1 It is essential that children are exposed to each of 6 structures of subtraction through their education, with comparison and then taking away being the primary understandings. Children should be taught to compare from Nursery age, so that they gain a sense of the relative size of numbers and amounts. From there they identify the difference between amounts and take away one from the other. These should both be taught at the first point of using subtraction, with a strong emphasis on the language being used. Combine sets of objects: Counting all the objects into a pot or bag. Count on beads along a bead string. Jump up in ones along a number line. Start with 2, then count up 5 more to reach the total. Or Start with 5, then count up 2 to reach the total. Line cubes up beneath a number track to show the link between physically adding the cubes and making the jumps up the line. Subtraction can be viewed in 6 structures: (This is not a hierarchy) Partitioning and taking away Comparison (difference) Finding the complement Counting back The inverse of addition. Bridging down through 10. The hierarchy for the language of comparison: Compare amounts. “There are more red cubes than blue cubes.” Compare numerically. “There are 4 more red cubes than blue.” “There are 16 red cubes but only 12 blue cubes.” Make the link to digits and symbols “16 is 4 more than 12.” 16 – 4 = 12 (because you have to take 4 away from 16 to make it equal 12.) For each method: First count all; count the first set one-by-one, then continue counting as you count the second set. Then count on; remember size of the first set and count on as you add the second set. Do these calculations on beadstrings to help children form the internal representation of adding beads being similar to counting along numbers on a number track.

Start with 9 on the bus, one more person gets on board. How many do you have now? Make the explicit link between one more on the bus and one more number along the number line. Which snake is longer/shorter? How much longer/shorter? Use this model for adding all single digit numbers. Just increase the number of jumps to fit in with the calculation. This should also be extended to adding a 2-digit number to another 2-digit number. 24+12= Above each ‘jump’, the children should write +1 to represent the size of the jump. As the children become more secure with the numberline method, they will start to use jumps of differing sizes. The recording of this will need to be adapted to their chosen size of jump. Ask the questions: (For the snakes, coins and number line) What’s the same? What’s different? What do you notice? Arrange the coins in lines to make the link between the coins lined up and numbers on a number track. 9 is further along the track than 6.

Addition - Phase 2 Partition numbers into tens and units: = (10+2)+(20+3) = (10+20) + (2+3) = 30+5 = 35. Start with partitioning numbers using Base 10, Cuisenaire Rods or Numicon into tens and units first, then record as numbers i.e. 53= Then use this knowledge to represent it on a number line. Finally, do it numerically. Subtraction – Phase 2 Once the children are aware that one number is bigger than another, explore ways of finding the difference between them. Everything that we do at this stage is focussed on helping children to construct their own internal representations of subtraction. These can take many forms, but will be based on one of the following: counting out (separating from), counting-back-from, counting-back-to, counting up (difference), inverse of addition or bridging-down-through-ten. (Thompson, 2008) 5 tens and 3 left over (Reinforces the idea of our number system being in base 10.) Counting Out (Separating from) In each case, link the separation from the whole with counting the beads on the bead strings as you take them away. This is then linked to counting back the numbers on a number line. Counting-back-from 3 less than 8 means that you count back three beads. Start with 8 and move three away. At the same time, count back 3 numbers along the number line from 8 to 5.

Counting-back-to Start with the first number, identify the target number and count how many beads you need to take away. Link this to identifying the numbers on a number line and counting back to the target number. 5, subtract something equals 3. Count back until you reach 3. How many have you subtracted? Count back 2 to reach the target of 3. = 54 The bead-string representation highlights the structure of the partitioning process. This can also be shown on a number line. Counting up (difference) – Step 1 This method exemplifies the gap in the number line between the two numbers of the calculation. Avoid the idea that “you put the small number at one end and the big number at the other”. Focus on the relative size of the numbers and identifying the ‘difference’ between them. 14 – 11 = Partitioning on the numberline Once the children have an understanding of place value and partitioning, you can add by partitioning on the number line. This can be by adding to make the multiple of ten and then add ‘lots of ten’ until you have added the second amount, or by adding tens to the original number.

Adding multiples of ten to any number The Inverse of addition This method relies on the children having had opportunities for the development of numerical reasoning. Understanding can be created by encouraging the child to make connections between the written calculation, language and the physical acts of moving a number of beads along the bead string or jumps along the number line. 24+12= +10 +2 Add the tens, then add the units. At first, add each ten one at a time, as the children’s understanding improves, they can add multiples of ten at a time. This should be extended to hundreds, and decimals too when appropriate. Bridging through ten with number bonds 24+12= +6 +6 To help to achieve this, use the following AfL questions and language: If, = 11, what might 11 – 4 = ? What do you notice about the number sentences 7+4=11 and 11-4=7 ? What’s the same and what’s different about them? Can you think of another number sentence that uses the numbers 11, 4 and 7? Can you write down the whole ‘calculation family’ for = 11? The next step is to use number bonds to ten in the calculation. In this case, the children add 6 to 24 to make 30, then add on the rest.

Partitioning and recombining . (The ‘Bow Tie’ method) Difference – step 2 (Adding in 10s) = = 51 85-19=66 +10 +10 +10 +10 +10 +10 +6 = = 338 (Bridging through 10) 85-19=66 = = 60 3 + 4 =7 = 67 +60 +5 +1 The children should be encouraged to draw their number lines with the ‘jumps’ as representative in size as possible. This method is then continued to be used with increasingly larger numbers and then decimal numbers.

Children will then be introduced to the informal pencil and paper methods that will build on their existing mental strategies. This is only to be taught in upper Key Stage 2, and only when the children have demonstrated that they have a secure understanding of place value, addition and are consistent when using the numberline strategies. Counting back – Step 2 (using place value_ Children begin to use empty number lines (or tracks) to count back. Initially they partition the amount they are subtracting into tens and ones. They then progress to using known number facts to confidently subtract in tens and units. They then progress to subtracting the whole group of tens in one jump. This then progresses to using written methods which will prepare them for the carrying method when it is appropriate. Children will not be encouraged to use decomposition for subtraction calculations. All subtraction calculations can be worked out accurately by using the numberline method. The method also supports the development of number sense, which can then be applied to different contexts in written calculation as well as in mental calculation too. The calculations audit that was completed in the summer term of 2014 showed that children from Reception to Year 6 were familiar with and happy to use the numberline for subtraction and also achieved a high level of success when using it too. This method is then continued with larger numbers (E.g. HTU) once the children are secure in their understanding of place value. The children should discover that calculating with higher numbers is no harder than doing so with tens and units, it just has more digits and more steps.

Models and Images for Understanding Multiplication and Division
Four different ways of thinking about multiplication are: as repeated addition, for example as an array, for example four rows of three objects as a scaling factor, for example, making a line 3 cm long four times as long. as the inverse of division. Children should experience multiplication in each of these forms during their primary education. Using multiplication in each of these ways in different contexts and in problem solving will help the children to increase their multiplicative fluency and their ability to reason too. Please see the Subject Leader for Mathematics for further clarification. Three different ways of thinking about division are: as sharing as grouping as the inverse of multiplication. Children should experience division in each of these forms from an early age. Children should be know whether they are sharing or grouping as it is easy to get very muddled. The answer is usually the same, however the conceptual understanding is different. When discussing multiplication, division should be used as it’s inverse, i.e. 2 x 3 = 6, so how many 2s are there in 6? Division – Phase 1 The language of Multiplication: The use of the multiplication sign can cause difficulties. Strictly, 3 × 4 means four threes or Read correctly, it means 3 multiplied by 4 (or 3, 4 times). However, colloquially it is read as ‘3 times 4’, which is or three fours. Fortunately, multiplication is commutative: 3 × 4 is equal to 4 × 3, so the outcome is the same. It is also a good idea to encourage children to think of any product either way round, as 3 × 4 or as 4 × 3, as this reduces the facts that they need to remember by half. (From ‘Teaching children to calculate mentally’ (Department for Education, 2010)) Sharing with objects 6 objects shared between 2 people. They get 3 objects each. 6 ÷ 2 = 3 Person 1 Person 2 Sharing is often taught in the earlier years with small numbers and can be calculated easily with objects that can be manipulated. As the numbers get higher, using high numbers of objects can lead to mistakes so other methods need to be used.

Multiplication – Phase 1 Grouping with objects 6 divided into groups of 2. There are 3 groups. Children’s understanding of multiplication starts with unitary counting. (See diagram on next page) using concrete materials. Such as counting cubes; 1, 2, 3, 4…. This of course is strongly linked to addition and the strategy of counting all. Once they can count single objects, they should start to count in twos, fives and tens. Each time, counting groups of objects as they say the number. Through chanting, seeing the numbers written down and representing the numbers using Numicon or Multilink cubes- in which the patterns in the numbers should be highlighted- the children will create their own internal representations of the multiplication facts. 2, 4, 6, 8, 10, 12, 14, 16, 18… 10, 20, 30, 40, 50, 60, 70… 6 ÷ 2 = 3 How many times does 2 go into 6? How many 2s are there in 6? x1 x1 x1 Counting all Counting on Line the objects up next to the numberline so that the children can see the connection between the line of objects and the numbers on the numberline. A strong link should be made between division on a numberline and multiplication on a numberline, as they are essentially the same. This also reinforces the concept of the inverse. Patterns: Numbers end in 2, 4, 6,8, 0. 10, 20, 30 is similar to 1, 2, 3 and each number ends in a 0.

Repeated addition Models of Multiplication and Division – The Inverses This model shows that the repeated addition structure of multiplication can be easily represented on a number line. As children count up in 2s, they can count up the jumps on the number line. Initially, this should be represented on a number track which displays each number from 1 to 20. All of the models of multiplication can and should be used to develop children’s understanding of division as the inverse of multiplication. Using these models should be employed where practical, for instance making or drawing arrays to illustrate the calculations 6÷2 or 20÷5 is much easier than doing the same thing for 250÷10. For higher numbers, using informal jottings and related number facts is a quick and efficient way of dividing by using what you know about multiplication. The number line method for division looks very similar to how it does for multiplication. The key difference is the starting point. For the calculation 96÷4, you are working out how many 4s there are in 96 by starting at 0 and seeing how many 4s there are until you get to 96. The related multiplication would be 4x24=96, in which you are multiplying 4 by 24 to find the answer. Equal Groups As part of helping the children to develop the concept of repeated addition, use the language of multiplication carefully. For the example above; =10 which is the same as 2x5=10, the language to use to aid conceptual development is: 2, 5 times. Using the phrases ‘5 lots of 2’ or ‘2 lots of 5’ can be confusing. If you made these as piles of cubes they would look very different, despite ultimately showing 10 cubes in total. This concept is called commutativity. a x b = b x a This can also be calculated on a numberline.

Repeated addition / equal groups - continued Division – Phase 2 3 x 4 = (3, 4 times) Division on a numberline 15 ÷ 3 = 5 x1 x1 x1 x1 Use other representations, such as bead strings, to support the understanding of division on the number line. = 12 Arrays 96 ÷ 4 = 24 3 x 4 = (3, 4 times) Division Fact Box List multiplication facts that can be used in the calculation. Fact Box 10x4=40 20x4=80 5x4=20 2x4=8 4x4=16 Showing multiplication as an array in Phase 1 is essential to help children see that multiplication is commutative and to enable them to really understand how the grid method works in Phase 2. x10 x10 x4 This array could show 3x4 or 4x3. It doesn’t matter whether you read it as a column of 3 dots, 4 times, or a row of 4 dots, 3 times. What is important is that the children see the commutativity.

Multiplication – Phase 2 Division with remainders Repeated addition / equal groups – Phase 2 25 ÷ 4 = 6 r1 Show the remainder in a different colour. 3 x 12 = (3, 12 times) x1 x1 x x1 x1 x1 x1 x1 x1 x1 x x1 x3 x3 r1 Move from the repeated addition/equal groups model in Phase 1, to using known number facts such as 3x2 or 3x5 to create fewer jumps along the number line, which will also reduce the chance of making mistakes in calculation. Numberline vesus more formal methods. This model of division on a numberline can be extended for any combination of numbers, regardless of their magnitude. This includes using decimals and fractions. The open nature of the model allows the mathematician to apply their own values to the line and to the size of each jump. The ‘bus stop’ method of division has been shown (by the Norfolk Calculations Research) to be confusing and to have a low success rate compared to the numberline method. The calculations audit (2014) showed the same. Children achieved a higher success rate by using the numberline. Focussing on one method throughout the school should create improvements in this area. x2 x5 x5 This can then be extended to using multiples of 10 to make the method more efficient. x10 x2

Models and Images for Understanding Multiplication and Problem Solving
Problem Solving Approaches Arrays The Grid Method – Part 1 Once children are able to represent multiplication as an array, they can start to divide up each of the numbers in the calculation to make finding the total easier. Using multiples of 10 is a preferred method, but it is not the only way. Children should be encouraged to see numbers as totals of more than one array. Different ways of calculating 3 x 12: Information on how to use the ‘Singapore Bar’ for problem solving will be added in this section. 2 2 2 2 2 2 3 5 5 2 3 10 2 3

Arrays The Grid Method – Part 2 Once children have experienced different ways of splitting up arrays, they should start to turn this into the conventional layout of the grid method for multiplication. It is important that the children are aware that the different rectangular sections are not the same size as each other. This understanding will be developed through the manipulation of arrays in part 1. Before calculating, the children should make an estimate of the anticipated answer. Adding up the numbers in the boxes should be done in the most efficient way. This may be different for each child. A preferred way is to find he total of the rows and then perform a vertical calculation on the right-hand-side of the grid. 12 x 35 = Estimate: >350 (Because 10 x 35 = 350) x 30 5 10 300 50 2 60 10 = 420 OR: = 350 = 70 300 120 420

Long Multiplication? The 2014 National curriculum makes many references to ‘Formal methods of calculation’ and ‘Long Multiplication’. The calculations audit (2014) showed that children experience a high level of success when using physical representations and jottings when they are using multiplication. Children should be taught to create different arrays and make the link between the objects that they have on their tables and the numberline that they are drawing. This in turn should help them to form a more secure understanding of the concept of multiplication and then would not have to reply on a digit based algorithm such as long multiplication. It is more important for children to be able to calculate accurately than to be able to follow an algorithm accurately. Marks in the Key Stage 2 SAT papers will be awarded for correct answers. There will be marks for use of formal methods, but only where the written answer is incorrect. If the answer is correct, then full marks will be awarded. (Information from the Profesional Network for Mathematics, Summer 2014.)

The North Norwich Cluster Calculations Policy

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